The stabilizers aforementioned are presently manufactured by a process which involves the production of litharge by blowing air through molten lead at very high temperatures. The litharge so produced is slurried with water and then with sulphuric acid under controlled conditions to cause the tri-basic lead sulphate to precipitate. This precipitate is separated and dried ready for use as a stabilizer. It is found that this process causes a high degree of atmospheric pollution, and that the final product contains an undesirably high concentration of unreacted lead. For instance in U.S. Pat. No. 3,323,859 dibasic lead salt stabilizers for PVC are manufactured by reacting litharge with dilute acetic acid, and the dibasic lead acetate so formed is reacted with sodium sulphate.
Various approaches have been taken to avoid the use of litharge in the production of stabilizers. In U.S. Pat. No. 452,386, metallic lead is converted to lead acetate by subjecting it to the alternate action of dilute acetic acid and of atmospheric air, then reacting the lead acetate with sulphuric acid.